Multimedia applications are increasingly utilised, particularly in mobile wireless applications.
In any such applications, an application must have access to an underlying protocol engine. A common protocol engine in IP (Internet protocol) telephony is the Session Initiation Protocol (SIP).
The most popular API specification for SIP is known as JAIN SIP API. It is a collection of Java interfaces implementing access to SIP protocol engines at a transaction level.
The JAIN SIP API is inflexible, hard to extend, underspecified and does not suit well proxy applications.
It is therefore an object of the present invention to provide an improved access for application to an underlying protocol engine, particularly but not exclusively for the case where that protocol engine is a SIP engine.